Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephalate (PET) material is a preform that is capable of being subsequently blown into a beverage container, such as, a bottle and the like.
As an illustration, injection molding of PET material involves heating the PET material (ex. PET pellets, PEN powder, PLA, etc.) to a homogeneous molten state and injecting, under pressure, the so-melted PET material is injected into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of the mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient enough to keep the cavity and the core pieces together against the pressure of the injected PET material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected PET material is then cooled to a temperature sufficient to enable ejection of the so-formed molded article from the mold. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be demolded, i.e. ejected off of the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, stripper rings and neck rings, ejector pins, etc.
When dealing with molding a preform that is capable of being blown into a beverage container, one consideration that needs to be addressed is forming a so-called “neck region”. Typically and as an example, the neck region includes (i) threads (or other suitable structure) for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an anti-pilferage assembly to cooperate, for example, with the closure assembly to indicate whether the end product (i.e. the beverage container that has been filled with a beverage and shipped to a store) has been tampered with in any way. The neck region may comprise other additional elements used for various purposes, for example, to cooperate with parts of the molding system (ex. a support ledge, etc.). As is appreciated in the art, the neck region can not be easily formed by using the cavity and core halves. Traditionally, split mold inserts (sometimes referred to by those skilled in the art as “neck rings”) have been used to form the neck region.
With reference to FIG. 1, a section along a portion of an injection mold 50 illustrates a typical molding insert stack assembly 60 that is arranged within a molding system (not depicted). The description of FIG. 1 that will be presented herein below will be greatly simplified, as it is expected that one skilled in the art will appreciate configuration of other components of the injection mold 50 that will not be discussed in the following description.
The molding insert stack assembly 60 includes a neck ring insert pair 52 that together with a mold cavity insert 54, a gate insert (not shown) and a core insert 61 define a molding cavity 61 where molding material can be injected to form a molded article. In order to facilitate forming of the neck region of the molded article and subsequent removal of the molded article, the neck ring insert pair 52 comprises a pair of complementary neck ring inserts that are mounted on adjacent slides of a slide pair 68. The slide pair 68 is slidably mounted on a top surface of a stripper plate 66. As commonly known, and as, for example, generally described in U.S. Pat. No. 6,799,962 to Mai et al (granted on Oct. 5, 2004), the stripper plate 66 is configured to be movable relative to a cavity plate assembly 74 and a core plate assembly (not depicted), when the mold in arranged in an open configuration, whereby the slide pair 68, and the complementary neck ring inserts mounted thereon, can be laterally driven, via a cam arrangement (not shown), for the release of the molded article from the molding cavity 61.
A typical neck ring insert has a body that includes a pair of projecting portions 70 that extend from a top and a bottom face of a flange portion 72 (i.e. a top projecting portion and a bottom projecting portion). Typically, the bottom face of the flange portion 72 abuts, in use, a top surface of the slide pair 68. Even though not depicted in FIG. 1, one skilled in the art will appreciate that the neck ring insert pair 52 comprises suitable fasteners for connecting to a respective one of the slide pair 68. In use, during certain portions of a molding cycle, the top projecting portion cooperates with a female receptacle disposed on the cavity plate assembly 74.
It is worthwhile noting that the top projecting portion traditionally performs two functions, which can be broadly categorized as an alignment function and a locking function. Generally speaking, the alignment function involves assisting, at least partially, in aligning the neck ring vis a vis the cavity plate 74. The locking function involves assisting, at least partially, in locking the neck rings in a locked position, for example, during an injection portion and in-mold cooling portion of a molding cycle, etc. It is known in the art to arrange the top projecting portion of the neck ring and the corresponding female receptacle of the cavity plate 74 in a pre-loaded arrangement. This pre-loading of the top projecting portion of the neck ring and the corresponding female receptacle can lead to premature fatigue and contributes to increased costs of operating the molding system due to a need to replace neck rings more often.
As is depicted in FIG. 1, the molding insert stack assembly 60 can be said to be associated with a stack height generally depicted in FIG. 1 at H1. As can be further seen in FIG. 1, a portion of the stack height H1 is contributed to by a height of the neck ring insert pair 52, depicted in FIG. 1 at H2. Put another way, it can be said that the height H2 of the neck ring insert pair contributes to an increased stack height H1. The increased stack height H1 results in several disadvantages associated with the molding insert stack assembly 60. Firstly, due to the increased stack height H1, there is a need to increase a length of the core insert 61. The increased length of the core insert 61 can lead to several problems, including increased potential for so-called “core shift” of the core insert 61. Secondly, the increased stack height H1 requires a molding system (not depicted) having a larger footprint.